Wind Load Characteristics Of Typical Bluff Body Sections Under Turbulent Flow

The free-stream turbulence significantly affects the measurement results of aerodynamic forces on structures in the wind tunnel tests.The aerodynamic characteristics of a structure are different in the flows with different turbulence parameters.The characteristics of wind load on the structures are flow-field-dependent.Therefore,the corresponding turbulence parameters must be exactly simulated to accurately measure the wind loads on a structure through wind tunnel tests.The turbulence intensity can be well simulated in the wind tunnel tests.However,large-scale turbulence cannot be exactly simulated in the tests,owing to the size limitation of conventional wind tunnels.Due to the simulation error of the turbulence integral scale,the extreme wind load measured by the wind tunnel test may be small,thus increasing the risk of structural damage.Therefore,it is necessary to put forward the corresponding theory to accurately evaluate the wind load on the structure.In this thesis,the influence of turbulence parameters on the wind load distribution characteristics of typical bluff body sections is studied by theoretical analysis and wind tunnel tests.Based on the quasi-steady theory,a fluctuating wind pressure prediction method based on two-wavenumber pressure admittance is established.The main research contents of this study are as follows:1.The current status of the research on wind load characteristics of typical bluff body sections is reviewed.The non-Gaussian properties of fluctuating wind pressure are introduced.The results of research on aerodynamic admittance function are summarized.Common empirical coherence function models of the aerodynamic forces are outlined.Some shortcomings in the current wind load research are also pointed out.2.Based on the theory of uniform isotropic turbulence,the uniformity and isotropy of gridgenerated turbulence are investigated.Based on the quasi-steady theory of fluctuating pressure,a two-wavenumber fluctuating pressure spectrum model is derived,and a method for identifying the two-wavenumber pressure admittance through the wind tunnel test is proposed.Thus,a fluctuating pressure prediction method is established based on the twowavenumber pressure admittance.3.The surface pressures of three typical bluff sections,namely the circular cylinder,square cylinder,and 5:1 rectangular cylinder,are measured in grid-generated turbulence with different turbulence intensities and different turbulence integral scales.The effects of turbulence intensity and turbulence integral scale on the mean wind pressure and fluctuating wind pressure distribution characteristics are analyzed.The effects of turbulence parameters on the non-Gaussian characteristics of fluctuating wind pressure are investigated.The probability density function of fluctuating wind pressure is fitted by using a variety of distribution functions,and the non-Gaussian peak factors and extreme wind loads under different turbulence parameters are obtained for different turbulence parameters.With the increase of the ratio of the turbulence integral scale to the characteristic size of the model,the fluctuating pressures and the extreme pressures increase continuously,and the skewness tends to become smaller while the kurtosis tends to become larger.4.The spectra and coherence function of the fluctuating wind pressure at representative pressure taps are obtained for three typical bluff body sections by the wind tunnel test.The influence of turbulence parameters on the fluctuating pressure correlation coefficient is analyzed.The two-wavenumber coherence function of fluctuating pressures is obtained by fitting the fluctuating pressure spanwise coherence function.The two-wavenumber spectra of fluctuating wind pressure at the stationary point of a circular cylinder,the separation point of a square cylinder,and the fluctuating wind pressure maximum point of a 5:1rectangular cylinder are calculated based on the relationship between the two-wavenumber coherence function and the two-wavenumber spectrum of fluctuating wind pressures.In addition,the spatial distribution of fluctuating wind pressure,fluid-structure interaction mechanism,and the pattern of the energy transition are further analyzed.With the increase in the ratio of the turbulence integral scale to the characteristic size of the model,the threedimensional effect of fluctuating pressure continues to be weakened.The spanwise correlation of fluctuating pressure is closer to the correlation of turbulent fluctuating wind speed.The frequency range of the two-wavenumber coherence function of the fluctuating pressure and the dominant energy of the two-wavenumber pressure spectrum is increasingly shifted to the low frequency.5.The two-wavenumber admittance of wind pressure is identified.The effects of turbulence intensity and turbulence integral scale on the two-wavenumber admittance of wind pressures are analyzed.The fluctuating wind pressure spectra,fluctuating wind pressure coefficient,and extreme pressure coefficient is predicted according to the fluctuating wind pressure prediction method based on the two-wavenumber admittance of wind pressures.The accuracy of the fluctuating wind pressure coefficient and extreme pressure coefficient predicted by the method of this study is discussed.The two-wavenumber admittance of wind pressure is independent of the turbulence integral scale,and the fluctuating wind pressure prediction method based on the two-wavenumber admittance of wind pressure proposed in this study has a high accuracy for the prediction of fluctuating pressure and extreme pressure.In addition,the relationship between the fluctuating wind pressure and the integrated parameters of turbulence is investigated,and the corresponding empirical equations are fitted.